Handrails for escalators, moving walkways and the like perform an essential function and serve as a safety component of the system. The handrail must provide a firm grip for the passenger and yet be sufficiently flexible to bend around various drive wheel mechanisms and as well as strong enough to withstand several hundreds of pounds of tensile force. Canadian Patent 898,726 discloses a widely used type of handrail construction having the standard C-shaped cross-section with longitudinally extending stretch inhibitor, body reinforcing fabric plies and slider member joined together in a molded rubber composition. The stretch inhibitor is provided as an integral band of several steel wire cables which are embedded in a rubber body matrix. The wire cables are under tension and are sufficient in number to meet the load specification of approximately 30,000 Newtons tensile strength and without extending under a load of 2230 Newtons by more than 0.1% in length.
As with most handrail constructions, the C-shaped cross-section handgrip is made from compounded synthetic rubber. There are multiple plies of rubber coated fabric provided within the handrail structure. The fabric layers may be positioned on either or both sides of the stretch inhibitor cables as for example, three of the plies lie above the stretch inhibitor cables whereas one of the plies lies underneath. Normally the inner surface layer of the handrail is of closely woven nylon, polyester or cotton fabric to provide minimal frictional contact with the escalator or moving walkway support structure and is commonly referred to as the slider ply. This construction allows sufficient flexibility for the handrail to travel along the escalator walkway system, particularly over the drive portion thereof. The C-shaped cross-section for the handrail is designed such that its inwardly directed lips engage a guide rail where sufficient tolerance is provided to allow easy movement and minimum wear of the slider fabric. However, the tolerance is such to prevent the ingress of fingers and clothing into the space between the moving handrail and the guide to prevent possible injury. To this end, regulatory authorities and manufacturers have set specifications on the inwardly directed lip space dimensions and the lip strength as determined by the handrail's resistance to distortion and the handrail's tendency to open up over its service life by virtue of the inwardly directed lips moving apart. However, it has been difficult for the industry to solve this problem in an economical manner. Most handrails on the market tend to become loose and hence unfit for continued use. As the handrail becomes loose, significant costs are then associated with down time to repair and/or replace the handrail and with potential personal injury liability.
A variety of handrail constructions are described in the patent literature which show various structures and some of which have in one way or another addressed the above problems, however, their solutions tend to be inadequate and therefoe not recommended.
U.S. Pat. No. 1,101,209 discloses a T-shaped handrail construction wherein the body of the handrail comprised several layers of rubber-coated fabric in a continuous band. The requirement for inextensibility and fitment to the rail-guide is met by incorporating three reinforcing ropes along the length of the handrail, i.e. one in the centre of the body and one along each edge of the T section.
U.S. Pat. No. 1,186,550 discloses the incorporation of a braided fabric layer into the coverstock which is close to the surface of the handrail. The locating of the fabric layer redistributes the bending stress and reduced premature cracking of the handrail.
U.S. Pat. No. 2,956,662 describes the use of a continuous U-shaped metal ribbon to give an inextensible handrail with high transverse strength and rigidity. However, in order to obtain flexibility in the longitudinal direction the ribbon needs to be perforated or slit laterally.
U.S. Pat. No. 3,623,590 lexplains that conventional C-shaped handrail tends to lose its resilience at the gripping edges due to the severe reverse bending experienced on some escalators. A flattened C-shape construction is described wherein the edge of the section is very flexible, and thus can endure a long duration of bending in both forward and backward modes.
In order to make a handrail of high lateral stiffness, U.S. Pat. No. 3,778,882 describes an intricate construction and process of injection molding rigid thermoplastic sections over a continuous wire reinforcement and molding over this composite a flexible cover.
U.S. Pat. No. 3,949,858 discloses a construction of a C-shaped handrail which uses three parallel inextensible cords as a stretch inhibitor and a fabric ply incorporated into the body stock near the inner surface to obtain lateral stiffness.
Published Japanese patent application (1977)-16629 discloses a design for C-shaped handrail in terms of the preferred section height, width, thickness, shape, in order to optimize the flexibility and lateral stiffness, particularly for use on escalators with a small diameter drive mechanism and to minimize power consumption.
U.S. Pat. No. 4,776,446 discloses a means of providing lateral stiffness to an extruded elastomeric handrail with continuous ribbon stretch inhibitor. This process involves placing a hard thermoplastic U-shaped liner into the handrail. It is necessary to incorporate slots into the liner in order to have longitudinal flexibility.
In a similar invention, U.S. Pat. No. 4,852,713 discloses a method for molding a polyurethane liner into a steel cord reinforced C-shaped handrail. Again, in order to achieve the required longitudinal flexibility it is necessary to have slots in the liner.
Published German patent applications DE 3,921,887, DE 3,921,888 and DE 3,930,351 disclose the incorporation of molded inserts, the use of low friction polymeric coatings and fire retardant compounds, and particularly, the use of five overlapping fabric layers to obtain sufficient lateral stiffness.
The industry still requires a simple expedient construction and method of manufacture of handrails to increase their lateral stiffness and lip strength while maintaining their longitudinal flexibility.